The functions of an EMA and a WMA are similar, they rely more heavily on the most recent prices and place less value on older prices. Traders use these EMAs and WMAs over SMAs if they are concerned that the effects of lags in data may reduce the responsiveness of the moving average indicator.
All moving averages have a significant drawback in that they are lagging indicators. Since moving averages are based on prior data, they suffer a time lag before they reflect a change in trend. A stock price may move sharply before a moving average can show a trend change. A shorter moving average suffers from less lag than a longer moving average.